Odometer

ABSTRACT

An odometer consisting of a frame attachable to a steerable, unpowered automobile wheel so as to be movable but not rotatable therewith, a roller carried by the frame on an axis parallel to the wheel axis and urged resiliently against the periphery of the tire of the wheel so as to be rotated when the wheel turns, and mechanism operable to count and indicate revolutions of the roller. The roller may be conical coaxially with its axis, and mechanism may be provided for moving the roller parallel to its axis, responsively to changes of air pressure in the tire, whereby to compensate for differences of tire diameter, and hence the distance travelled for each rotation thereof, resulting from different tire pressures.

[ June 26, 1973 United States Patent 91 Finley Primary Examiner-StephenJ. Tomsky Attorney-John A. Hamilton ODOMETER Inventor: Carl E. Finley,401 E. Fourth Street,

Lamar, Mo. 64759 Dec. 8, 1971 [21] 7 Appl. No.: 205,968

[57] ABSTRACT An odometer consisting of a frame attachable to a [22]Filed:

steerable, unpowered automobile wheel so as to be movable but notrotatable therewith, a roller carried by the frame on an axis parallelto the wheel axis and urged resiliently against the periphery of thetire of the wheel so as to be rotated when the wheel turns, andmechanism operable to count and indicate revolutions 3 5 1 w M63 I in c.r mmm L W i C10 WH t e Uhm 1:1] 2 8 555 .l.[.l.

of the roller. The roller may be conical coaxially with References CitedUNITED STATES PATENTS its axis, and mechanism may be provided for movingthe roller parallel to its axis, responsively to changes of air pressurein the tire, whereby to compensate for differences of tire diameter, andhence the distance travelled for each rotation thereof, resulting fromdifferent tire pressures.

Nowak et al. Ferro, Sr.....

972 Murphy, Jr. et al.

n a m H T 9 6 9 9 Claims, 5 Drawing Figures ODOMETER This inventionrelates to new and useful improvements in odometers, or instruments formeasuring distance travelled, by automobiles, trucks, and othervehicles.

The primary object of the present invention is the provision of anodometer capable of measuring the distance travelled with greateraccuracy than has heretofore been possible. The odometers with whichautomotive vehicles are customarily furnished may be sufficientlyaccurate for general purposes, but often a greater accuracy isdesirable. For example, a telephone line construction contractor maydesire to use a vehicle odometer for laying out and properly spacing thepositions at which to set telephone poles in the ground. For thispurpose, the individual readings to be taken range normally from 100 to500 feet, and the accuracy should be within 1% percent. The usualodometer is virtually useless in this application. It indicates tenthsof miles as the smallest increment, and while smaller increments can beestimated, they cannot be estimated with the required accuracy. Even ifthey could be read directly in feet, it would still be subject toseveral causes of inaccuracy. First, it usually operates by a geareddrive from the vehicle transmission, and so in effect merely countsrevolutions of the driven wheels of the vehicle. The driven vehiclewheels have a sometimes substantial degree of slippage relative to theroad surface, particularly during periods of acceleration ofdeceleration, or on dirt, gravel or other loose surfaced roads, and thisslippage introduces error into the odometer reading. Second, it does notcompensate for tirewear. Tire wear gradually reduces the tire diameterand circumference, and hence the road distance travelled for eachrevolution thereof, so that any odometer which merely counts wheelrevolutions will give gradually more and more excessive readings. Third,it does not compensate for variationsin the air pressure of the tire.All tires compress or yield to some degree where they engage the road,and the effective tire diameter, and distance travelled per revolutionthereof thus varies with the air pressure, higher pressures increasingthe effective tire diameter and distance travelled per revolution, andvice versa.

Accordingly, the present odometer includes means operable to eliminateor greatly reduce all of the above enumerated sources of inaccuracy.Absolute accuracy in measuring the travel of a vehicle supported byyieldable pneumatic tires is not possible so far as is now known, butthe present device will provide accuracy well within the acceptablelimits of i A percent over 'any distance, and in most cases even greateraccuracy.

Other objects are simplicity and economy of construction, and efficiencyand dependability of operation.

With these objects in view as well as other objects which will appear inthe course of the specification, reference will be had to theaccompanying drawing, wherein:

FIG. 1 is a fragmentary edge elevational view of a vehicle wheel showingan odometer embodying the present invention mounted operatively thereon,with parts broken away,

FIG. 2 is a fragmentary side elevational view of the parts shown in FIG.1,

FIG. 3 is an enlarged, fragmentary sectional view taken on line III-IIIof FIG. 2, and including a schematic wiring diagram,

FIG. 4 is an enlarged, fragmentary sectional view taken on line IVIV ofFIG. 2, and

FIG. 5 is a sectional view of the roller taken on line VV of FIG. 3.

Like reference numerals apply to similar parts throughout the severalviews, and the numeral 2 applies generally to a vehicle wheel having apneumatically inflated tire 4, and including a rigid wheel disc 6removably secured to the brake drum 8 by threaded lugs 10 and lug nuts12, all as common and well known in the art. Wheel 2 may be assumed tobe a front wheel, since it is desirable that the odometer be mounted ona nonpowered wheel, and since in most vehicles it is the front wheelswhich are not powered. If the vehicle has a front-wheel drive, theodometer would be mounted on a rear wheel. The front wheels are alsogenerally the steerable wheels, and for this reason wheel 2 is shownmounted rigidly on a steering arm 14 affixed to a steering pin 16disposed at right angles to the wheel axis and carried for axialoscillation by a portion of the wheel suspension frame 18. Thus when pin16 is turned by the steering mechanism (not shown), wheel 2 turns tosteer the vehicle.

The odometer as contemplated by the present invention includes acup-shaped hub member 20 fitted coaxially over the grease cap 22 (seeFIG. 4) of the wheel hub, and having integral ears 24 at its inner endwhich are engaged on lugs 10 and secured by lug nuts 12. Formedintegrally with the hub is an outwardly extending stub shaft 26, alsocoaxial with wheel 2. The odometer also includes a frame indicatedgenerally by the numeral 28 and being generally of inverted U-shape,including a pair of parallel, vertical legs 30 and 32 disposedrespectively adjacent the inner and outer faces of wheel 2, in spacedrelation therefrom, and a shaft 34 extending between the upper ends ofsaid legs, above tire 4 of the wheel and parallel to the wheel axis,said shaft being rigidly affixed at its ends to said legs. Leg 30 istelescopically extensible in length, including a lower section 30Aaffixed at its lower end, as by pin 36, to steering pin 16, so as toturn therewith, and an upper section 30B telescoped slidably over saidlower section and secured at its upper end, as by pin 38, to a headfixture 40. A helical tension spring 42 is disposed within said leg,being attached at its upper and lower ends to pins 44 and 46 affixedrespectively in leg sections 308 and 30A, whereby said leg isresiliently biased toward a shorter length. Leg sections 30A and 30B aresufficiently non-circular in cross-sectional contour to prevent relativerotation therebetween.

Similarly, outer leg 32 consists of slidably telescoped lower and uppersections 32A and 32B having therein a tension spring 48 attached at itsupper end to a pin 50 affixed in leg section 32B and at its lower end toa pin 52 fixed in leg section 32A. Leg 32 is affixed at its upper end,as by pin 54, in a head fixture 56, and at its lower end, as by pin 58,in a bearing fixture which is rotatably mounted on stub shaft 26 of hubmember 20 by a ball bearing 62 and secured thereon by a collar 64 pinnedto said shaft. It will be appreciated, however, that frame 28 does notrotate with wheel 2, said frame being affixed by its leg 30 to steeringpin 16, and that stub shaft 26, which does rotate with the wheel,rotates within bearing fixture 60. Shaft 34 extends between headfixtures 40 and 56, and is affixed therein by pins 66 and 68respectively.

Mounted on shaft 34 is a carrier sleeve 70. Said sleeve is keyed to saidshaft, as by key 72, so as to be slidable along said shaft, but notrotatable therein. The end portion of said sleeve closer to frame leg 30is enlarged in diameter, and telescopically engaged over a stop sleeve74 which is fixedly pinned to shaft 34 at 76. A helical compressionspring 78 is positioned about shaft 34, bearing at one end againstsleeve 74, and at its opposite end against an internal shoulder 80 ofsleeve 70, whereby to urge sleeve 70 outwardly along shaft 34, or to theleft as viewed in FIG. 3.

Mounted on carrier sleeve 70 is a roller assembly indicated generally bythe numeral 82. Said assembly includes a pair of end walls 84 and 86disposed concentrically with shaft 34 and rigidly interconnected by tierods 88 extending parallel to the shaft, and a hollow roller shell 90coaxial with the shaft and rotatably mounted at its respective ends onend walls 84 and 86, by means of ball bearings 92. Said end walls areconnected to carrier sleeve 70 by keys 94 and 96 respectively, so as tobe 'slidable along said sleeve, but not rotatable thereon. Roller shell90 is preferably externally conical in form, with its smaller end to theleft as viewed in FIG. 3, for a reason which will presently appear.

Carrier sleeve 70 is extended outwardly from end wall 86 of the rollerassembly, and is provided at its extended end with an integrally,radially extending ear 98 in which is rotatably mounted a screw 100.Said screw is parallel to shaft 34, and is threaded into end wall 86.Thus, by turning said screw, roller assembly 82 may be shiftedaxiallyalongthe carrier sleeve in either direction. Mounted in end wall 84 ofthe roller assembly is an air cylinder member 102, which is disposedinternally of the roller assembly, but opens outwardly through end wall84, it axis being parallel to but downwardly offset from shaft 34.Operable in said cylinder is a fixed piston 104 formed integrally withhead fixture 56 of frame leg 32, a packing device 106 forming anair-tight seal therebetween. An air passageway 108 of said piston opensinto cylinder 102, and communicates with a lateral neck 110 of saidpiston adjacent frame leg 32. One end of a flexible tube 112 isconnected by fitting 114 to neck 110, and the opposite end of said tubeis connected by fitting 116 to a rigid tube 118 fixed in an integral ear120 of bearing fixture 60 by set screw 122. Tube 118 is angled to extendthrough a bore 124 formed axially in stub shaft 26, in order that saidshaft may revolve while said tube remains stationary, and

into the interior of hub member 20. Within said hub member, tube 118 isconnected by an air-tight rotary swivel coupling 126 (see FIG. 4), whichis coaxial with wheel 2, to a rigid tube 128 which is fixed in a wall ofsaid hubmember by nuts 130, extending exteriorly of said hub. A flexibletube 132 is connected to the outer end of tube 128 by fitting 134, andits opposite end is connected by fitting 136 with the usual valve stem138 of tire 4. It will be understood that fitting 136 is provided withan internal projection or the like operable to open the usual valve ofstem 138 as said fitting is attached to said stem. Thus the interior oftire 4 is connected at all times to the interior of air cylinder 102,and'the cylinder pressure will always equal the tire pressure. Pressurein cylinder 102 urges roller assembly 82 to the right as viewed in FIG.3, against the bias of spring 78, until the total air pressure force isbalanced by the spring pressure.

Affixed in end wall 84 of the roller assembly, interiorly of rollershell 90, is an electric proximity switch 140, which is not detailed butis standard and well known in the art, consisting broadly of an electricswitch operable to be actuated each time a magnet is brought into closeproximity therewith. In this case, the magnet, indicated at 142, ispermanently mounted in a boss 144 formed on the interior surface ofroller shell 90, so as to be moved past switch 140, in close proximity,once during each revolution of said shell. The lead wires 146 and 148 ofswitch are contained in a cable 150 extending outwardly from end wall 84through a seal 152, and as diagrammed in FIG. 3, are connected in serieswith a power source 154, which may be the usual vehicle battery, and anelectrically actuated counter device 156 which is operable to advanceone digit each time switch 140 is actuated. Preferably, each digitadvance of the counter should accurately indicate a small but convenientunit of vehicle travel, such as one foot. It will be understood thatcounter 156 is preferably mounted in the vehicle at a position forconvenient viewing by the driver.

In operation, it will be seen that with the device mounted as shown,springs 42 and 48 of frame legs 30 and 32 urge and maintain roller shell90 firmly against the tread of tire 4 to insure a firm, non-slipengagement therebetween, so that as the vehicle travels, said rollerturns, its revolutions being counted and recorded by counter 156 toindicate the distance of vehicle travel, and that the indicated distancewill be accurate so long as the effective circumference and diameter ofroller 90 bears the proper ratio to the effective circumference anddiameter of the tire.

If counter 156 is to indicate travel in feet, it is convenient to use aroller having an effective circumference of 1 foot, since the surfacetravel of the roller is equal to the surface travel of the tire tread,and since the surface travel of thetire tread is generally equal to thedistance of vehicle travel. Any reduction of the effective treadcircumference, resulting from tread wear,'is automatically reflected inthe reading of counter 156, since the reduction of tread circumferenceresults both in a reduction of the vehicle travel per revolution of thewheel 2, and also in a reduction of the number of turns of roller 90 perrevolution of wheel 2.

However, thesurface travel of roller 90 will seldom if ever bepreciselyequal to the distance of vehicle travel under ordinary circumstances. Inthe first place, all pneumatically inflated tires are flattened ordeformed at least to some degree in the areas thereof engaging the roadsurface at any given moment, so that the vehicle is actually travellingon wheels of smaller effective radius, and hence travelling a lesserdistance per wheel revolution, than would be the case if the effectiveradius of the wheel were that actually engaging roller 90, which doesnot depress or deform the tire to any comparable degree. Moreover, thedegree of yielding of the tire against the road surface is differentwith different tires, even with equal air pressures, due to differencesof tire construction. Also, the degree of tire yield varies in any tirewith the air pressure of the tire, lower pressure permitting still moretire yield, and hence a further reduction in the distance travelled perrevolution of the wheel. Hence, for a high degree of accuracy, it willbe apparent that some means should be provided for adjusting the ratioof the rotary speed of roller 90 to that of wheel 2. In the presentodometer, this adjustment is made manually by turning screw 100,

and automatically in response to changes of tire pressure by means ofcylinder 102 and spring 78. Either of these means is operable to moveroller 90 axially along shaft 34, either to the right as shown in FIG.3, whereby to bring a portion of roller 90 'of lesser diameter intoengagement with tire 4 to produce more turns of the roller perrevolution of wheel 2, or to the left whereby to bring a portion of theroller of greater diameter into engagement with the tire to producefewer roller turns per wheel revolution.

for indicating what change of counterreading will be.

produced over a 1,000 foot course, for each turn or fraction of a turnof screw 100. This calibration is carried out with tire 4 inflated to apressure midway in a range or ordinary and acceptable pressures, said at25 psi as the midpoint of a 20- 30 psi range. Tests have shown that withonly this manual adjustment, with the roller otherwise fixedagainstmovement along shaft 34, readings within a range of iripercent'accuracy can reliably be obtained from counter 156, as long asthe tire pressure is maintained within the 20-30 psi range.

Still greater accuracy is obtained, compensating for any change of tirepressure within or even outsideof the range given above, by theinteraction of cylinder 102 and spring 78. If the tire pressure drops,reducing the distance of vehicle travel per revolution of the wheel, thepressure in cylinder 102 drops, allowing roller 90 to be moved to theleft by spring 78, bringing a larger portion of the roll'er'into playagainst the-tire, and producing correspondingly fewer turns of theroller per revolution of the wheel. Conversely, if the tire pressureincreases, as on hot road surfaces, the increased pressure in cylinder102 forces the roller to the right against spring 78, bringing a smallerportion of the roller into play against the tire. This produces morerevolutions of the roller. per revolution of the wheel, to compensatefor the resulting greater distance of vehicle travel per wheelrevolution.

The accuracy of this automatic pressure-responsive system depends on theproper correlation of the degree of taper of the roller to the modulusof spring, 78 and area of cylinder 102, within the expected range ofpressure variation. These relationships can be developed mathematically,though ultimate accuracy will be affected by unavoidable production-variations. Also, some'inaccuracy of ultimate readings will'result fromvarious imponderable factors, such as irregular tire wear, and wheelbouncing or vibration, which can cause minute rippling of the tireandslippage of the roller thereagainst. Nevertheless, tests have shownthat the pressure-responsive adjusting means can reliably reduce byone-half any error in the counter reading which remains after manualcalibration has been performed, thereby producing an accuracy in therange of i V4 percent, which is amply close for most purposes.

Of course, if roller 90 has a one-foot circumference, and if it isequipped with only one proximity switch 140 and magnet 142, as shown,then the least increment of vehicle travel readable on counter 156 isone foot, not fractions thereof. This factor in itself can introduce anerror of almost a foot into the reading. While this degree of errorwould ordinarily be acceptable, greater accuracy can be obtained eitherby reducing the circurnference of roller 90 to some smaller fraction ofa foot, or, in a roller of the same diameter, placing either moreswitches or more magnets within the roller, angularly distributed aboutshaft 34. Proximity switches 140 are available which can be reliablyactuated at least times per second. With the one-foot roller as shown,this permits accurate recording at vehicle speeds in excess of 30 milesper hour, which corresponds to 44 feet per second. Actually, however,the vehicle speeds recommended for use with devices of this type areusually in the area of only 15 miles per hour, in order to reduce errorcausedby bouncing of the wheel on the road surface, or rippling of thetire tread.

Accuracy of the present odometer is improved by the fact that it ismountable on a non-powered vehicle wheel, which is much less likely toslip or slide on the road surface than a powered wheel. Frame 28 isineffect mounted directly on the axle of the wheel, or memther insurenon-slip engagement of the roller with the tire. When the wheel 2 is asteering wheel pivotable about a generally vertical steering axis, theattachment of frame 28 to a portion of the wheel suspensionmovable aboutsaid steering axis, as shown, insures preservation of parallelismbetween the wheel and roller axes.

While I have shown and described a specific embodiment of my invention,it will be readily apparent that many minor changes of structure andoperation could be made without departing from the spirit of theinvention.

What I claim as new and desire to protect by Letters Patent is:

1. An odometer for use in connection with an automotive vehicle. havinga ground-engaging wheel equipped with a pneumatically inflated tire,said vehicle wheel being a non-powered, steerable wheel,'the suspensionthereof including parts pivotal about a generally vertical axis relativeto the vehicle'to accomplish steering thereof, said odometer comprising:

a. a frame, I

b. means mounting said frame on said pivotal wheel suspension meansadjacent said wheel, whereby said frame turns with said wheel on itsvertical steering axis, and is movable with the axis of said wheeltransversely thereto, but is not rotatable with said wheel,

c. a' roller carried rotatably by said frame so that its periphery has anon-slip engagement with thetread periphery of said tire, its axis beingparallel with the axis of said wheel, whereby said roller is rotated byrotation of said vehicle wheel, and

d. means operable to count and record the revolutions of said roller.

2. An odometer for use in connection with an automotive vehicle having aground-engaging wheel equipped with a pheumatically inflated tire, saidodometer comprising:

a. a frame,

b. means mounting said frame on a portion of said vehicle adjacent saidwheel so as to be movable with the axis of said wheel transverselythereto, but not rotatable with said wheel,

c. a roller carried rotatably by said frame so that its periphery has anon-slip engagement with the tread periphery'of said tire, its axisbeing parallel with the axis of said wheel, whereby said roller isrotated by rotation of said vehicle wheel,

d. means operable'to count and record the revolutions of said roller,and means operable to adjust the ratio of the rotative speed of saidroller to the rotative speed of said wheel.

3. An odometer is recited in claim 2 wherein said adjusting means ismanually operable.

4. An odometer as recited in claim 2 wherein said adjusting means isautomatically responsive to changes of the air inflation pressure ofsaid tire, whereby said ratio of roller and tire speeds is varied ingenerally inverse relation to changes in said air pressure.

5. An odometer as recited in claim 2 wherein said adjusting meanscomprises:

a. manually operable means for changing the effective diameter of saidroller in engagement with said tire, and

b. pressure-sensitive means operable responsively to changes of airpressure in said tire to change the effectivediameter of said roller inengagement with said tire.

6. An odometer as recited in claim 2 wherein said roller is externallyfrustro-conical in form, coaxially with its axis of rotation, andwherein said adjusting means comprises means operable to move saidroller parallel toits axis, selectively in either direction, relative tosaid frame, whereby to bring portions thereof of different diametersinto engagement with said tire.

7. An odometer as recited in claim 6 wherein said means for moving saidroller parallel to its axis is manually operable.

8. An odometer as recited in claim 6 wherein said means for moving saidroller parallel to its axis includes pressure-sensitive meansinterconnected with and responsive to air pressure within said tire.

9. An odometer for use in connection with an automotive vehicle having aground-engaging wheel equipped with a pneumatically inflated tire, saidodometer comprising:

a frame including a fixed shaft parallel with the wheel axis and spacedoutwardly from the tread of said tire,

b. means mounting said frame on a portion of said vehicle adjacent saidwheel so as to be movable with the axis of said wheel transverselythereto, but not rotatable with said wheel,

0. a carrier sleeve mounted on said shaft for movement axially alongsaid shaft but secured against rotation thereon,

d. roller end discs carried on said sleeve for movement axiallytherealong but secured against rotation thereon e. a roller carried bysaid end discs for rotation coaxially with said shaft, said roller beingexternally conical in form to have larger and smaller ends, and having anon-slip engagement with the tread periphery of said tire, whereby saidroller is rotated by rotation of said vehicle wheel,

f. manually operable means for moving said roller end discs axiallyalong said carrier sleeve,

g. resilient means urging said carrier sleeve axially along said shafttoward the smaller end of said roller,

h. a pneumatic cylinder carried by the roller end disc at the smallerend'of said roller, parallel with said shaft, and opening outwardly,

i. a piston carried fixedly by said frame and projecting operably intosaid cylinder,

j. means interconnecting said cylinder to the interior of said tire,whereby the air pressure of said tire enters said cylinder and forcessaid carrier sleeve and roller end discs axially along said shaft towardthe larger end of said roller, against the bias of said resilient means,and

k. means operable to count and record the revolutions of said roller.

1. An odometer for use in connection with an automotive vehicle having aground-engaging wheel equipped with a pneumatically inflated tire, saidvehicle wheel being a non-powered, steerable wheel, the suspensionthereof including parts pivotal about a generally vertical axis relativeto the vehicle to accomplish steering thereof, said odometer comprising:a. a frame, b. means mounting said frame on said pivotal wheelsuspension means adjacent said wheel, whereby said frame turns with saidwheel on its vertical steering axis, and is movable with the axis ofsaid wheel transversely thereto, but is not rotatable with said wheel,c. a roller carried rotatably by said frame so that its periphery has anon-slip engagement with the tread periphery of said tire, its axisbeing parallel with the axis of said wheel, whereby said roller isrotated by rotation of said vehicle wheel, and d. means operable tocount and record the revolutions of said roller.
 2. An odometer for usein connection with an automotive vehicle having a ground-engaging wheelequipped with a pheumatically inflated tire, said odometer comprising:a. a frame, b. means mounting said frame on a portion of said vehicleadjacent said wheel so as to be movable with the axis of said wheeltransversely thereto, but not rotatable with said wheel, c. a rollercarried rotatably by said frame so that its periphery has a non-slipengagement with the tread periphery of said tire, its axis beingparallel with the axis of said wheel, whereby said roller is rotated byrotation of said vehicle wheel, d. means operable to count and recordthe revolutions of said roller, and means operable to adjust the ratioof the rotative speed of said roller to the rotative speed of saidwheel.
 3. An odometer is recited in claim 2 wherein said adjusting meansis manually operable.
 4. An odometer as recited in claim 2 wherein saidadjusting means is automatically responsive to changes of the airinflation pressure of said tire, whereby said ratio of roller and tirespeeds is varied in generally inverse relation to changes in said airpressure.
 5. An odometer as recited in claim 2 wherein said adjustingmeans comprises: a. manually operable means for changing the effectivediameter of said roller in engagement with said tire, and b.pressure-sensitive means operable responsively to changes of airpressure in said tire to change the effective diameter of said roller inengagement with said tire.
 6. An odometer as recited in claim 2 whereinsaid roller is externally frustro-conical in form, coaxially with itsaxis of rotation, and wherein said adjusting means comprises meansoperable to move said roller parallel to its axis, selectively in eitherdirection, relative to said frame, whereby to bring portions thereof ofdifferent diameters into engagement with said tire.
 7. An odometer asrecited in claim 6 wherein said means for moving said roller parallel toits axis is manually operable.
 8. An odometer as recited in claim 6wherein said means for moving said roller parallel to its axis includespressure-sensitive means interconnected with and responsive to airpressure within said tire.
 9. An odometer for use in connection with anautomotive vehicle having a ground-engaging wheel equipped with apneumatically inflated tire, said odometer comprising: a frame includinga fixed shaft parallel with the wheel axis and spaced outwardly from thetread of said tire, b. means mounting said frame on a portion of saidvehicle adjacent said wheel so as to be movable with the axis of saidwheel transversely thereto, but not rotatable with said wheel, c. acarrier sleeve mounted on said shaft for movement axially along saidshaft but secured against rotation thereon, d. roller end discs carriedon said sleeve for movement axially therealong but secured againstrotation thereon e. a roller carried by said end discs for rotationcoaxially with said shaft, said roller being externally conical in formto have larger and smaller ends, and having a non-slip engagement withthe tread periphery of said tire, whereby said roller is rotated byrotation of said vehicle wheel, f. manually operable means for movingsaid roller end discs axially along said carrier sleeve, g. resilientmeans urging said carrier sleeve axially along said shaft toward thesmaller end of said roller, h. a pneumatic cylinder carried by theroller end disc at the smaller end of said roller, parallel with saidshaft, and opening outwardly, i. a piston carried fixedly by said frameand projecting operably into said cylinder, j. means interconnectingsaid cylinder to the interior of said tire, whereby the air pressure ofsaid tire enters said cylinder and forces said carrier sleeve and rollerend discs axially along said shaft toward the larger end of said roller,against the bias of said resilient means, and k. means operable to countand record the revolutions of said roller.